Stop-valves, gate-valves and ball-valves

Filed Under: Do it yourself, Home repair, Plumbing    by: ITC

These are all plumbing fittings that in different ways do precisely the same thing, which is to regulate the flow of water through pipes. Each of the three types of valve performs an important function in your water system, and it is therefore in your interest to know not only what they do and how they do it, but also how to put right any of the faults to which they are prone.

Stop-valves

Your main stop-valve is perhaps the single most important plumbing fitting in your house. In the event of almost any plumbing emergency the very first thing that you should do is turn it off. This will stop the flow of water into your house and reduce the extent of any damage. Looking like a very basic brass tap, your main stop-valve will be found set into the rising main not far from the point where this pipe enters your house. Often it will be located under the kitchen sink.

If your house is fairly old then it could be that it won’t be provided with a main stop- valve. If this is the case, then you will have to use the local water authority’s stop-valve instead. You will find it under a hinged metal flap set into your garden path or the pavement outside your property. This sort of stop- valve usually has a specially-shaped handle that can only be turned with one of the water authority’s turnkeys. So that you can deal promptly with any emergency you should make sure that you either have one of these turnkeys. or at least that you have ready access to one. However, both for the sake of convenience and because specialist gadgets like turnkeys have a habit of disappearing when they’re most needed, you may decide to install a main stop-valve yourself – not a difficult task if the rising main is made of copper pipe.

The internal construction of a stop-valve is identical to that of an ordinary tap, and so it is prone to the same types of faults (sees Ready Reference). But one further trouble that may afflict your stop-valve – which doesn’t crop up with ordinary taps – is that of jamming in the open position as a result of disuse. It’s a problem cured simply by applying penetrating oil to the spindle. However, you can prevent this happening by closing and opening the stop-valve regularly, and by leaving it fractionally less than fully open – a quarter turn towards closure will do.

Gate-valves

Whereas stop-valves are always fitted to pipes that are under mains pressure, gate- valves are used on pipes that are only subject to low pressure. They are therefore found on hot and cold water distribution pipes and on those of the central heating system. Gate valves differ from stop-valves in as much as they control the flow of water through them, not with a washered valve, but by means of a metal plate or ‘gate’. You can distinguish them from stop-valves by the fact that their valve bodies are bigger, and by their wheel as opposed to crutch – handles. Due to the simplicity of their internal construction gate- valves require little attention (see Ready Reference). Unlike stop-valves, which have to be fitted so that the water flowing through them follows the direction of an arrow stamped on the valve body, you can install a gate- valve either way round.

Mini stop-valves

Mini stop-valves are useful little fittings that you can insert into any pipe run. Their presence enables you to re-washer or renew a tap or ball-valve or repair a water-using appliance such as a washing machine without disrupting the rest of your water system. They can aiso be used to quieten an excessively noisy lavatory flushing cistern that is fed directly from the rising main, since by slowing down the flow of water to the ball-valve you can reduce the noise without materially affecting the cistern’s rate of filling after flushing. You usually fit a mini stop-valve immediately before the appliance that it is to control: and they can be turned off and on either with a screwdriver, or by turning a small handle through 180°.

Ball-valves

Ball-valves are really just self-regulating taps designed to maintain a given volume of water in a cistern. While there are a number of different patterns they all have a float-not necessarily a ball these days – at one end of a rigid arm which opens or closes a valve as the water level in the cistern falls or rises. There are basically two types of ball-valves: the traditional type, generally made of brass, in which the water flow is controlled by a washered plug or piston; and the type that has been developed more recently in which the flow is controlled by a large rubber diaphragm housed within a plastic body.

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